Effects of Cathode GDL Gradient Porosity Distribution along the Flow Channel Direction on Gas-Liquid Transport and Performance of PEMFC.

The gas diffusion layer (GDL) is an important component of proton exchange membrane fuel cells (PEMFCs), and its porosity distribution has considerable effects on the transport properties and durability of PEMFCs. A 3-D two-phase flow computation fluid dynamics model was developed in this study, to numerically investigate the effects of three different porosity distributions in a cathode GDL: gradient-increasing (Case 1), gradient-decreasing (Case 3), and uniform constant (Case 2), on the gas-liquid transport and performance of PEMFCs; the novelty lies in the porosity gradient being along the channel direction, and the physical properties of the GDL related to porosity were modified accordingly. The results showed that at a high current density (2400 mA·cm-2), the GDL of Case 1 had a gas velocity of up to 0.5 cm·s-1 along the channel direction. The liquid water in the membrane electrode assembly could be easily removed because of the larger gas velocity and capillary pressure, resulting in a higher oxygen concentration in the GDL and the catalyst layer. Therefore, the cell performance increased. The voltage in Case 1 increased by 8% and 71% compared to Cases 2 and 3, respectively. In addition, this could ameliorate the distribution uniformity of the dissolved water and the current density in the membrane along the channel direction, which was beneficial for the durability of the PEMFC. The distribution of the GDL porosity at lower current densities had a less significant effect on the cell performance. The findings of this study may provide significant guidance for the design and optimization of the GDL in PEMFCs.

Pore-Scale Modeling of Microporous Layer for Proton Exchange Membrane Fuel Cell: Effective Transport Properties.

A microporous layer (MPL) is a transition layer with a porous material structure, located between the gas diffusion layer (GDL) and catalyst layer (CL) in a proton exchange membrane fuel cell (PEMFC). It not only significantly improves electron transfer and heat conduction in membrane electrode assembly, but also effectively manages liquid water transport to enhance the fuel cell performance. The MPL is usually coated on one side of the GDL. The fragile nature of MPL makes it challenging to characterize the effective transport properties using experimental methods. In this study, a stochastic numerical method is implemented to reconstruct the three-dimensional microstructure of an MPL consisting of carbon particles and PTFE. The reliability of the MPL reconstructed model is validated using experimental data. The relationship between the effective transport properties and the compression strain is obtained using the Pore Scale Model (PSM), while the relationship between the liquid water saturation and capillary pressure is solved by Lattice Boltzmann Method (LBM). The effective transport properties in the MPL are then imported into the two-phase flow fuel cell model. It is found that the effective transport parameters in MPL obtained by PSM and LBM can improve the accuracy of the model calculation. This study provides an effective method to reconstruct the microstructure of MPL that can generate precise MPL transport parameters for utilization in various PEMFC performance prediction models.

Purification and comparison of soluble and membrane-bound polyphenol oxidase from potato (Solanum tuberosum) tubers.

Enzymatic browning greatly affects the quality of potato products. Polyphenol oxidase (PPO) is the enzyme mainly responsible for potato enzymatic browning. PPO has soluble polyphenol oxidase (sPPO) and membrane-bound polyphenol oxidase (mPPO) forms. In this study, the properties of sPPO and mPPO were investigated in potato tubers. The molecular weight of potato sPPO and mPPO were estimated to be 69 kDa in the form of homodimers in vivo. The mass spectrometry results showed that the purified sPPO and mPPO protein in potato tubers was mainly tr|M1BMR6 (Uniprot). The optimum pH for sPPO and mPPO was 6.5, and the optimum temperatures were 20 and 30 °C, respectively. The Michaelis constant (Km) and maximum unit enzyme activity (Vmax) of sPPO were 6.08 mM and 2161 U/S when catechol was used as the substrate, whereas those of mPPO were 2.95 mM and 2129.53 U/S, respectively. The mPPO had stronger affinity to the substrate catechol than sPPO, whereas pyrogallic acid was stronger affinity for sPPO. Ascorbic acid and sodium sulfite were inhibitors of sPPO and mPPO, respectively. After understanding the different binding states of polyphenol oxidase, different inhibitors and treatment methods can be used to treat the enzyme according to different enzymatic properties, so as to achieve a greater degree of Browning control. These results will provide a theoretical basis for regulating PPO activity to reduce enzymatic browning during potato processing.

Microstructure Reconstruction and Multiphysics Dynamic Distribution Simulation of the Catalyst Layer in PEMFC.

Due to the complexity of both material composition and the structure of the catalyst layer (CL) used in the proton-exchange membrane fuel cell (PEMFC), conjugated heat and mass transfer as well as electrochemical processes simultaneously occur through the CL. In this study, a microstructure model of CL was first reconstructed using images acquired by Nano-computed tomography (Nano-CT) of a real sample of CL. Then, the multiphysics dynamic distribution (MPDD) simulation, which is inherently a multiscale approach made of a combination of pore-scale and homogeneous models, was conducted on the reconstructed microstructure model to compute the corresponded heat and mass transport, electrochemical reactions, and water phase-change processes. Considering a computational domain with the size of 4 um and cube shape, this model consisting of mass and heat transport as well as electrochemical reactions reached a stable solution within 3 s as the convergence time. In the presence of sufficient oxygen, proton conduction was identified as the dominant factor determining the strength of the electrochemical reaction. Additionally, it was concluded that current density, temperature, and the distribution of water all exhibit similar distribution trends, which decrease from the interface between CL and the proton-exchange membrane to the interface between CL and the gas-diffusion layer. The present study not only provides an in-depth understanding of the mass and heat transport and electrochemical reaction in the CL microstructure, but it also guides the optimal design and fabrication of CL components and structures, such as improving the local structure to reduce the number of dead pores and large agglomerates, etc.

Two-Dimensional Simulation of the Freezing Characteristics in PEMFCs during Cold Start Considering Ice Crystallization Kinetics.

Cold start is one of the major issues that hinders the commercialization of polymer electrolyte membrane fuel cells (PEMFCs). In this study, a 2D transient multi-physics model is developed to simulate the cold start processes in a PEMFC. The phase change between water vapor, liquid water, and ice in the catalyst layers (CLs), micro porous layer (MPLs), and gas diffusion layers (GDLs) is also investigated, particularly the effect of ice crystallization kinetics when supercooled liquid water changes into ice. The factors affecting the different operating conditions and structural features of the membrane electrode assembly (MEA) are investigated. The results show that when the start temperature is -20 °C or higher, ice formation is delayed and the formation rate is decreased, and supercooled liquid water permeates from the CL into the MPL. For an MEA with relatively high hydrophobicity, the water permeation rate is high. These results can enable a PEMFC to start at subzero temperatures. The effect of ice crystallization kinetics is negligible when the fuel cell is started at -30 °C or below.

Histone deacetylase 6 promotes skin wound healing by regulating fibroblast migration and differentiation in aged mice / 生理学报

Skin wound healing tends to slow down with aging, which is detrimental to both minor wound recovery in daily life and the recovery after surgery. The aim of current study was to explore the effect of histone deacetylase 6 (HDAC6) on wound healing during aging. Cultured human dermal fibroblasts (HDFs) and mouse full-thickness skin wound model were used to explore the functional changes of replicative senescent dermal fibroblasts and the effect of aging on skin wound healing. Scratch wound healing assay revealed significantly decreased migration speed of senescent HDFs, and BrdU incorporation assay indicated their considerably retardant proliferation. The protein expression levels of collagen and HDAC6 were significantly decreased in both senescent HDFs and skin tissues from aged mice. HDAC6 activity inhibition with highly selective inhibitor tubastatin A (TsA) or HDAC6 knockdown with siRNA decreased the migration speed of HDFs and considerably suppressed fibroblast differentiation induced by transforming growth factor-β1 (TGF-β1), which suggests the involvement of HDAC6 in regulating fundamental physiological activities of dermal fibroblasts. In vivo full-thickness skin wound healing was significantly delayed in young HDAC6 knockout mice when compared with young wild type mice. In addition, the wound healing was significantly slower in aged wild type mice than that in young wild type mice, and became even worse in aged HDAC6 knockout aged mice. Compared to the aged wild type mice, aged HDAC6 knockout mice exhibited delayed angiogenesis, reduced collagen synthesis, and decreased collagen deposition in skin wounds. Together, these results suggest that delayed skin wound healing in aged mice is associated with impaired fibroblast function. Adequate expression and activity of HDAC6 are required for fibroblasts migration and differentiation.

Identification of the prognostic value of elevated ANGPTL4 expression in gallbladder cancer-associated fibroblasts.

BACKGROUND: Cancer-associated fibroblasts (CAFs) with different gene profiles from normal fibroblasts (NFs) have been implicated in tumor progression. Angiopoietin-like protein 4 (ANGPTL4) has been shown to regulate tumor angiogenesis and metastasis, and predict poor prognosis. However, the ANGPTL4 expression in CAFs, especially in gallbladder CAFs (GCAFs) and its relationship with patient prognosis is unclear. METHODS: Affymetrix gene profile chip analysis in vitro was performed to detect the different gene expression profiles between GCAFs and NFs. RT-qPCR, immunohistochemistry, and western blotting were performed to investigate the different expression levels of ANGPTL4 in GCAFs/NFs in vitro and in an in vivo nude mouse model of xenograft tumors. Finally, the ANGPTL4 expression was investigated in the stroma of different lesion tissues of the human gallbladder by immunohistochemistry, especially the expression in GCAFs in vivo by co-immunofluorescence, and their prognostic significance in patients with gallbladder cancer (GBC) was assessed. RESULTS: ANGPTL4 was upregulated in both GCAFs in vitro and in the xenograft stroma of nude mice in vivo, and its expression was also significantly upregulated in human GBC stroma co-localized with the interstitial markers fibroblast secreted protein-1 and α-smooth muscle actin. In addition, the elevated ANGPTL4 expression in GCAFs was correlated with tumor differentiation, liver metastasis, venous invasion and Nevin staging, and GBC patients with an elevated ANGPTL4 expression in GACFs were found to have a lower survival rate. CONCLUSIONS: Increased ANGPTL4 expression in GCAFs correlates with poor patient prognosis, which indicates a potential therapeutic target for human GBCs.

Gallbladder cancer-associated fibroblasts promote vasculogenic mimicry formation and tumor growth in gallbladder cancer via upregulating the expression of NOX4, a poor prognosis factor, through IL-6-JAK-STAT3 signal pathway.

BACKGROUND: Cancer-associated fibroblasts (CAFs) and vasculogenic mimicry (VM) play important roles in the occurrence and development of tumors. However, the relationship between CAFs and VM formation, especially in gallbladder cancer (GBC) has not been clarified. In this study, we investigated whether gallbladder CAFs (GCAFs) can promote VM formation and tumor growth and explored the underlying molecular mechanism. METHODS: A co-culture system of human GBC cells and fibroblasts or HUVECs was established. VM formation, proliferation, invasion, migration, tube formation assays, CD31-PAS double staining, optic/electron microscopy and tumor xenograft assay were used to detect VM formation and malignant phenotypes of 3-D co-culture matrices in vitro, as well as the VM formation and tumor growth of xenografts in vivo, respectively. Microarray analysis was used to analyze gene expression profile in GCAFs/NFs and VM (+)/VM (-) in vitro. QRT-PCR, western blotting, IHC and CIF were used to detected NOX4 expression in GCAFs/NFs, 3-D culture/co-culture matrices in vitro, the xenografts in vivo and human gallbladder tissue/stroma samples. The correlation between NOX4 expression and clinicopathological and prognostic factors of GBC patients was analyzed. And, the underlying molecular mechanism of GCAFs promoting VM formation and tumor growth in GBC was explored. RESULTS: GCAFs promote VM formation and tumor growth in GBC; and the finding was confirmed by facts that GCAFs induced proliferation, invasion, migration and tube formation of GBC cells in vitro, and promoted VM formation and tumor growth of xenografts in vivo. NOX4 is highly expressed in GBC and its stroma, which is the key gene for VM formation, and is correlated with tumor aggression and survival of GBC patients. The GBC patients with high NOX4 expression in tumor cells and stroma have a poor prognosis. The underlying molecular mechanism may be related to the upregulation of NOX4 expression through paracrine IL-6 mediated IL-6/JAK/STAT3 signaling pathway. CONCLUSIONS: GCAFs promote VM formation and tumor growth in GBC via upregulating NOX4 expression through the activation of IL-6-JAK-STAT3 signal pathway. NOX4, as a VM-related gene in GBC, is overexpressed in GBC cells and GCAFs, which is related to aggression and unfavorable prognosis of GBC patients.

[Chewing Screen and Interventions for Older Adults].

Seeing older adults with nasogastric (NG) tubes in nursing homes is an unfortunately widespread phenomenon in Taiwan. NG tubes deprive the wearer of the tastes, smells, and joys of food and have been associated with malnutrition and increased susceptibility to aspiration pneumonia. In our studies, we found that 43% of nursing home residents in Taiwan are intubated with an NG tube and revealed a significant lower body mass index and hypoalbuminemia in these residents. In addition, the prevalence of dysphagia in residents of long-term care institutions was found to be greater than 60%. Older adults with dysphagia usually rely on liquid diets, which are frequently low in fiber, fruit, vegetable, and cereal contents. It is well known that diets low in fiber and vegetables increase the risks of constipation and cardiovascular events in older adults. A low intake of plant flavanols may also make older adults more susceptible to chronic inflammation. A high intake of red meats, eggs, or seafood may nurture gut microorganisms that catabolize carnitine and choline to trimethylamine-N oxide and which have been significantly linked to cardiovascular diseases and increased mortality. In contrast, eating plant vegetables and cereals is known to nurture better microbiota that produce short chain fatty acids, which, in turn, nurture enterocytes and improve immunity and brain health. Thus, the aims of this article are to demonstrate how to assess elders with chewing difficulty and dysphagia and to provide functional food scales for the classification, training, and care of active-aging nutrition. Through this article, we anticipate helping long-term care caregivers master key techniques for training and caring for elders with chewing difficulties and/or dysphagia. This article is also expected to 1) improve the nutrition of elders and satisfaction with feeding, 2) improve chewing and dysphagia care and training in long-term care institutions, and 3) avoid NG tube institution and aspiration pneumonia. The suggestions of this article may be used in the future to assist long-term care units across the interdisciplinary care providers teams to promote chewing instruction, swallowing care training, and active aging, appropriate nutrition, and health in older adult populations.

Inhibition of autophagy by chloroquine enhances the antitumor activity of gemcitabine for gallbladder cancer.

Gemcitabine (GEM), as an anti-metabolic nucleoside analog, has been shown to have anticancer effects in various tumors, but its chemotherapy resistance is still an important factor leading to poor prognosis of cancer patient. A large number of studies in recent years have shown that autophagy plays an important role in the chemotherapy sensitivity of many tumors, including pancreatic, non-small cell lung, and bladder cancer. However, whether GEM causes autophagy in gallbladder cancer (GBC) and whether it is related to chemotherapy resistance is unknown. In the present study, we demonstrated that GEM induced apoptosis and protective autophagy in GBC cells, which may be related to the AKT/mTOR signaling pathway, and GEM in combination with autophagy inhibitor chloroquine can strengthen the cytotoxic effect of GEM on GBC in vitro and in vivo. These findings showed that both autophagy and AKT/mTOR signals were engaged in GBC cell death evoked by GEM, GBC patients might benefit from this new treatment strategy, and molecular targeted treatment in combination with autophagy inhibitors shows promise as a treatment improvement.

Insight into norcantharidin, a small-molecule synthetic compound with potential multi-target anticancer activities.

Norcantharidin (NCTD) is a demethylated derivative of cantharidin, which is an anticancer active ingredient of traditional Chinese medicine, and is currently used clinically as a routine anti-cancer drug in China. Clarifying the anticancer effect and molecular mechanism of NCTD is critical for its clinical application. Here, we summarized the physiological, chemical, pharmacokinetic characteristics and clinical applications of NCTD. Besides, we mainly focus on its potential multi-target anticancer activities and underlying mechanisms, and discuss the problems existing in clinical application and scientific research of NCTD, so as to provide a potential anticancer therapeutic agent for human malignant tumors.

Improving Oxygen Reduction Performance by Using Protic Poly(Ionic Liquid) as Proton Conductors.

Improving catalytic performance of the oxygen reduction reaction (ORR) of Pt/C catalysts is essential for reducing Pt-loading and the according cost of proton exchange membrane fuel cells (PEMFCs). Herein, we report a new conceptual design of catalyst layers to improve the ORR performance of Pt/C catalysts by replacing perfluorosulfonated ionomers with protic poly(ionic liquid) as a proton conductor. The specific activity of the designed catalyst at 0.9 V under acidic conditions is over three times higher than that of catalyst using Nafion as the proton conductor. Furthermore, the durability test reveals that the introduction of protic poly(ionic liquid) ionomers can protect Pt nanoparticles against aggregation during potential cycles, but it is less durable than Nafion because of the nature of hydrocarbons. Nevertheless, we believe that replacing perfluorosulfonated ionomers with protic poly(ionic liquid) as proton conductors could be a promising strategy to design an efficient cathode for low Pt-loading PEMFCs.

Bi-metallic boride electrocatalysts with enhanced activity for the oxygen evolution reaction.

Rational design and understanding of the intrinsic mechanism are critical to develop highly active and durable electrocatalysts. In this study, a series of bi-metallic boride catalysts based on Ni and Co were prepared, and their activities were evaluated. The synthesised Co-10Ni-B catalyst exhibited excellent activity for water splitting in a 1 M KOH electrolyte. The overpotential was 330 mV at a current density of 10 mA cm-2, better than previously reported mono-metallic borides and even IrO2. The synergistic effect of Co and Ni was proved by X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy. The facile formation of critical intermediates CoOOH and NiOOH during the catalytic processes and a significant increase in surface area owing to the introduction of a second metal into mono-metallic boride were attributed to the superior catalytic performance of catalysts for the oxygen evolution reaction. A Co-10Ni-B-sp catalyst with a higher surface area than the Co-10Ni-B catalyst was also synthesised to evaluate the effect of a high surface area on the catalytic activity. A lower overpotential of 310 mV at a current density of 10 mA cm-2 was achieved.

Degradation of Silicone Rubbers as Sealing Materials for Proton Exchange Membrane Fuel Cells under Temperature Cycling.

Gaskets are compressed in proton exchange membrane fuel cells (PEMFCs) to keep fuel, oxidant and coolant within their respective regions and are very important for sealing and maintaining electrochemical performance of fuel cells during their long-term operation. It has been proved that the gas leakage caused by the failure of the gaskets following long-term operation is one of the main reasons for PEMFC performance degradation. In this work, degradation of silicone rubbers, the potential gasket materials for PEMFCs, were investigated in the simulated PEMFC environment solution, weak acid solution, de-ionized water and air, respectively, under alternating temperature cycling from -20 °C to 90 °C. The changes in hardness, weight, chemical properties, mechanical behavior and surface morphology of the samples of silicone rubbers were studied after a certain number of temperature cycles. The results show that with the increase in temperature cycles, the hardness of the samples increases and the weight of the samples decreases gradually. Scanning electron microscopy reveals that cracks and caves constantly appear on the surface of the samples. Attenuated total reflection Fourier transform infrared spectra (ATR-FTIR) results demonstrate that the surface chemistry changes via de-crosslinking and chain scission in the backbone due to the exposure of samples to the environments over time under alternating temperature cycles.

Self-assembly synthesis of a unique stable cocoon-like hematite @C nanoparticle and its application in lithium ion batteries.

A novel cocoon-like Fe2O3@C nanoparticle was fabricated via a facile hydrothermally molecular self-assembly procedure. Compared to bare Fe2O3 nanoparticles, the carbon coated Fe2O3 nanoparticles exhibit higher specific capacity, excellent rate capacity and cyclic stability as the anode in lithium ion batteries. These cocoon-like Fe2O3@C nanoparticles carry enhanced lithium storage properties with a reversible capacity of 358mAhg-1 after 150 cycles under the current density of 1000mAg-1, while the carbon-free bare Fe2O3 can only deliver a much lower capacity of 127.6mAhg-1 with a continuously decreasing trend. The excellent performance of Fe2O3@C is attributed to the coated carbon layers, which not only enhance the electronic conductivity but also reduce the stress upon the Fe2O3 nanoparticles caused by the volume change during the charge/discharge process.

Engineered Graphene Materials: Synthesis and Applications for Polymer Electrolyte Membrane Fuel Cells.

Engineered graphene materials (EGMs) with unique structures and properties have been incorporated into various components of polymer electrolyte membrane fuel cells (PEMFCs) such as electrode, membrane, and bipolar plates to achieve enhanced performances in terms of electrical conductivity, mechanical durability, corrosion resistance, and electrochemical surface area. This research news article provides an overview of the recent development in EGMs and EGM-based PEMFCs with a focus on the effects of EGMs on PEMFC performance when they are incorporated into different components of PEMFCs. The challenges of EGMs for practical PEMFC applications in terms of production scale, stability, conductivity, and coupling capability with other materials are also discussed and the corresponding measures and future research trends to overcome such challenges are proposed.

Self-Organized 3D Porous Graphene Dual-Doped with Biomass-Sponsored Nitrogen and Sulfur for Oxygen Reduction and Evolution.

3D graphene-based materials offer immense potentials to overcome the challenges related to the functionality, performance, cost, and stability of fuel cell electrocatalysts. Herein, a nitrogen (N) and sulfur (S) dual-doped 3D porous graphene catalyst is synthesized via a single-row pyrolysis using biomass as solitary source for both N and S, and structure directing agent. The thermochemical reaction of biomass functional groups with graphene oxide facilitates in situ generation of reactive N and S species, stimulating the graphene layers to reorganize into a trimodal 3D porous assembly. The resultant catalyst exhibits high ORR and OER performance superior to similar materials obtained through toxic chemicals and multistep routes. Its stability and tolerance to CO and methanol oxidation molecules are far superior to commercial Pt/C. The dynamics governing the structural transformation and the enhanced catalytic activity in both alkaline and acidic media are discussed. This work offers a unique approach for rapid synthesis of a dual-heteroatom doped 3D porous-graphene-architecture for wider applications.

Metal-Organic-Framework-Derived Dual Metal- and Nitrogen-Doped Carbon as Efficient and Robust Oxygen Reduction Reaction Catalysts for Microbial Fuel Cells.

A new class of dual metal and N doped carbon catalysts with well-defined porous structure derived from metal-organic frameworks (MOFs) has been developed as a high-performance electrocatalyst for oxygen reduction reaction (ORR). Furthermore, the microbial fuel cell (MFC) device based on the as-prepared Ni/Co and N codoped carbon as air cathode catalyst achieves a maximum power density of 4335.6 mW m-2 and excellent durability.

High viscosity to highly dispersed PtPd bimetallic nanocrystals for enhanced catalytic activity and stability.

A facile high-viscosity-solvent method is presented to synthesize PtPd bimetallic nanocrystals highly dispersed in different mesostructures (2D and 3D structures), porosities (large and small pore sizes), and compositions (silica and carbon). Further, highly catalytic activity, stability and durability of the nanometals have been proven in different catalytic reactions.